136: 
$ 7. Finally we will draw attention for a moment to the analogy 
of the corresponding Röntgen-patterns of the su/phates of magnesium, 
nickel and zinc, erystallising with 7H,O in the rhombie-bisphenoi- 
dical class. The parameters of these salts are doubtless immediately 
comparable : 
Magnesiumsulphate: MgSO,, 7H,0; a:b: ¢ = 0,9901 : 1: 0,5709; spec. 
gravity: 1,677; x: >: wo =6,315: 6,379 : 3.641. 
Nickelsulphate  NUSO 3 EO); a bro 01981 5%: 1: 0;5656;'spec. 
gravity: 1,955; y: w: w = 6,255 : 6,373 : 3,605. 
Zincsulphate ZS (HO; arbre = 0.980471 + 0/5631; spec: 
gravity : 1,976: y: w : w— 6,282 : 6.408 : 3,608. 
We were not able to get any of these patterns in a form suitable 
for reproduction: in the case of all these suiphates the images were 
very feeble, so that finally only some of their stereographical projec- 
tions could be obtained in a form, which was at least somewhat 
satisfactory for the purpose of comparing them. 
They are reproduced in fig. 26, 27, and 28 on Plate IV, namely 
as images only parallel to (001), and in fig. 24 and 25 only these 
parallel to (010) for the maynesium-, and the niche/salt, because the 
images parallel to (010) of the zcsalt were hitherto only obtained 
in an abnormal *) form. 
Although even in this case a certain analogy of corresponding 
patterns seems to be undeniable, the differences between the images 
appear however to be quite appreciable, — which must doubtless 
be partially explained by the photos not being very beautiful, and for 
this purpose somewhat rudimentary, but which on the other hand is, 
without any doubt, partially caused by the fact, that also here the 
distribution of the intensities of the corresponding spots in these 
patterns, is in every case different. It may be remarked here, that 
this fact, — although in a less high degree, — appears also from 
the Röntgen-patterns of pyrite and hauerite, published by Ewarp and 
FRIEDRICH *). 
$ 8. If now we review once more the results obtained in this 
investigation, we can draw with some certainty from them the 
following conclusions : 
a. The general structure of the Rontgen-patterns of analogously 
orientated sections of isomorphous crystals, appears to be a closely 
related one. It is confirmed by the previous study, that the view, 
5 Vid: H. Haca and F. M. Jaeger, these Proceed. 18. p. 570 and 571. (1915). 
2) P. P. Ewarp and W. Frieprrcn, Ann. der Physik (4). 44. 1183. (1914). 
SS 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
